This invention relates generally to spring units for use in mattresses, spring upholstered furniture and the like and, more particularly, to an improved pocketed coil spring unit and associated method of manufacturing such a spring unit.
A well known type of spring assembly includes a number of discrete coil springs, each of which is enclosed in a fabric pocket in a length of folded fabric material. Longitudinal axes of the coil springs are generally parallel with one another so that the top and bottom end turns of the coil springs define top and bottom faces of the spring unit. A spring assembly can be fabricated from such a spring unit by forming rows of the pocketed coil springs and binding or adhering the individual rows together to form a mattress or spring assembly.
This type of spring assembly is commonly referred to as a pocketed spring unit due to the fact that each spring is contained within an individual pocket of fabric material. The construction of strings of pocketed coil springs in each pocket is well known in the art and, for example, disclosed in U.S. Pat. No. 4,439,977 which is hereby incorporated by reference in its entirety. The system disclosed in that patent includes a spring coiler which forms a coil spring which is subsequently compressed and inserted between the plies of folded pocketing fabric material. Other systems for manufacturing pocketed coil spring assemblies are disclosed in PCT patent application Ser. No. WO94/18116 and U.S. patent application Ser. No. 08/927,051 filed Sep. 10, 1997, each of which are expressly incorporated herein by reference.
Pocketed spring units are generally recognized to have a unique and particular luxurious feel to them and mattresses manufactured of such pocketed spring units provide a feeling of softness without lacking spring resilience or support. Mattresses and similar articles constructed of pocketed spring units are often considered a high-end type of product because of the added benefits and features of the pocketed coil springs. Mattresses and the like of this type can be more costly to manufacture and assemble as a result of the considerable amount of time and labor which is involved in their manufacture, together with the fact that the method of fabrication and assembly of such pocketed spring units can be complicated, particularly in an automated process.
One particular aspect of the commercial production of pocketed spring units and the associated mattresses or the like is the handling of such units in the factories. The manipulation and movement of the various components of the spring unit from station to station or various areas of the factories can be cumbersome, difficult and inconvenient depending on the particular production facilities and assembly techniques.
Additionally, while pocketed spring units are considered to provide a combination of softness and support, the ability to economically posturize a spring unit or mattress of pocketed spring coils has heretofore been unavailable. Posturization provides zones of support within a mattress. For example, the middle regions of the mattress, which typically support a person""s torso, often require a firmer more resilient support while other areas of the mattress which support the feet and head of a person require a softer feel.
Therefore, there is a need for an improved pocketed spring unit and associated method of manufacture which offers the advantages of posturization of the spring unit without the higher manufacturing costs, production difficulties and inefficiencies associated with known spring units.
These and other objectives of the invention have been obtained in an improved pocketed coil spring unit and associated method of manufacturing such a spring unit according to this invention. In one embodiment, the pocketed coil spring unit of this invention and associated method combines top and bottom sheets with side gluing or bonding of the rows of pocketed coil springs. By using this combination, a posturized spring unit is produced in a commercially effective manufacturing process.
The pocketed coil spring unit includes narrow strips of non-woven material extending generally perpendicular to the rows of pocketed coil springs. Supply rolls of the non-woven sheets are positioned on the top and bottom of the coil unit being assembled. Strings or rows of pocketed coil springs are serially added to the forming coil unit which is positioned between top and bottom conveyors. Adhesive is applied to the top and bottom sheets to adhere the sheets to the top or bottom surface of the pocketed coil springs as the rows are added to the forming coil spring unit. The strips of top and bottom sheets are positioned as required on the coil spring unit and, in one embodiment, just one sheet in the center of the spring unit on the top and bottom faces is utilized to provide posturization of the spring unit, mattress or the like. The top and bottom sheets are applied to the top and bottom, respectively, of the coil spring unit at locations where a firmer, more resilient support foundation is desired. On the remaining sections of the coil spring unit, side gluing or bonding of the adjacent rows or strings of pocketed coil springs is utilized to provide the flexible benefits of such a construction. Specifically, in one embodiment, the sidewalls of the pocketed coil springs are sprayed with adhesive or otherwise bonded to the sidewalls of pocketed coil spring units in adjacent rows. Known spring units which are side glued or bonded to the adjacent rows of coil spring units typically do not have the top and bottom sheets bonded thereto.
One advantage of this invention is the ability to efficiently and conveniently handle the coil spring unit in the factories in that it will act like a top/bottom glued construction while still providing the flexible benefits of a side glued unit. Moreover, this invention offers the ability to customize or posturize the spring unit with various zones of resiliency and support. As such, this invention provides increased benefits during the manufacturing of pocketed coil spring units while offering advantages, including posturization, not currently available in known pocketed coil spring units, mattresses or the like.